Periodic time function signals are required, for example, as reference signals in coherence receivers for receiving, for example, so called "Chirp" signals. In such coherence receivers a received signal, which may be corrupted by noise, is multiplied in the detection process, on one hand with the reference signal itself, and on the other hand with the reference signal shifted by 90.degree. for eliminating, or at least reducing the interference.
A coherence receiver is described, for example in U.S. Pat. No. 3,937,899 of Denenberg, in col. 2, lines 49 to 69, and col. 3, lines 1 to 43, however, only for the relatively simple case where the reference signal is a pure sinusoidal or cosinusoidal signal, the amplitudes of which are stored in a memory.